1. Field of the Invention
This invention relates to an image forming apparatus, such as a laser printer, for forming an image on an image bearing member according to data supplied from a host unit and, more particularly, to an image forming apparatus compatible with other kinds of image forming apparatuses.
2. Description of the Related Art
Recently, in an image forming apparatus for forming an image on an image bearing member, a laser printer has been developed and put into practical use. For example, U.S. Pat. No. 4,681,425 discloses this laser printer design. The laser printer serves as an output device for a host unit. Also, the laser printer includes a buffer memory for temporarily storing image data supplied from the host unit. In response to a printer command from the host unit, the laser printer performs an image forming operation to form an image on the image bearing member according to image data stored in the buffer memory.
Also, in addition to image data supplied from the host unit, this laser printer receives a printer control language which is adapted for operating the laser printer. For example, the printer control language represents such things as where to draw a box or a circle, when to start printing and so on. However, different kinds of laser printers have their own printer control language. Thus, in order to make the laser printer compatible with other laser printers, the laser printer is designed with its own native printer control language and also with the ability to emulate other laser printers. This function is called an emulation or a printer emulation. Thus, this laser printer may emulate the printing operation of other kinds of laser printers by selecting the printer emulation of the laser printer.
In a conventional laser printer, when an operator changes the printer emulation so as to emulate another printer according to the image data supplied from the host unit which is stored in the buffer memory, the stored image data always is erased from the buffer memory. Thus, when the operator wants to print the erased image data after the printer emulation is changed, it is necessary to receive the same image data from the host unit again. Therefore, in the conventional laser printer, it is very troublesome to print the image data stored in the buffer memory before the printer emulation is changed.